Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a first embodiment of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second embodiment thereof.

Outermost broken lines in the FIGURES show a display screen or portion thereof, and form no part of the claimed design. Broken lines in the FIGURES show portions of a graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with graphical user interface, as shown and described. 